Itsukushima, also known as Miyajima (宮島, Shrine Island, is where the famed giant "floating" torii gate rests upon the inland Seto Sea. Many visitors come to pay their respects and watch the tide ebb and flow underneath the shrine. At low tide, the water recedes beyond the large torii, and visitors can walk out upon the seabed and explore the gate up close.
Itsukushima is quite rural and unpopulated. You can take a tram to the top of Mount Misen (弥山) and embark on several short hikes among the forest and smaller shrines.
Also popular on the island are its maple trees. During autumn season, the island is blanketed in red and orange foliage, and visitors can try the various snacks and sweets inside which maple leaves are baked.
Beware the deer, though. They will eat your things.